1. Field of the Invention
The present invention relates to a private branch exchange system, and more particularly to a private branch exchange system using a plurality of mobile stations.
2. Description of the Related Art
Conventionally, in a private branch exchange system, one department is assigned one or a plurality of extension numbers which are used to make a wired-based call on the premises.
However, in such a private branch exchange system, since one department is simply assigned one or a plurality of extension numbers, a telephone call intended for a user belonging to the department may be answered by another user. In this case, extra time is required for putting the intended user on the line.
Additionally, when a called party is away from his desk, a calling party must make a call again.
To address these disadvantages, in recent years, a private branch exchange system is contemplated in which each user of the private branch exchange system is assigned one mobile station for performing wireless communication. It is thus possible to eliminate the time taken for putting an intended user on the line and to receive an incoming call even when a user is away from his desk.
Mobile stations assigned to respective users have different extension numbers respectively which are used to make a call among the mobile stations.
In the prior art private branch exchange system using mobile stations as mentioned above, each user of the private branch exchange system is assigned one mobile station having a unique extension number, so that a common extension number throughout one department is not provided as in the prior art wired private branch exchange system.
Thus, in the case of a call directed to a department, a mobile station is called by using an extension number of one of users belonging to the department. If the mobile station is busy or outside a service area, a disadvantage occurs in that another mobile station is called by using an extension number of another user belonging to the department.
Additionally, a disadvantage exists in that, if a mobile station is busy, a caller must make another call later since one mobile station is assigned only one extension number.
When a mobile station is busy or outside a service area, a call directed thereto may be transferred to another mobile station. However, the transfer function depends on the setting operations by a user, and the disadvantages as mentioned above occur if a user has forgotten to set the transfer function.